Abstract
Entomopathogenic nematodes (EPNs) of the genera Heterorhabditis and Steinernema (Rhabditida: Heterorhabditidae and Steinernematidae), are natural enemies of numerous insects, which employ bacterial symbionts, Photorhabdus and Xenorhabdus (Enterobacteriales: Morganellaceae), respectively; to rapidly kill their insect host. They are among the frequently used beneficial biocontrol agents of numerous insect pests and constitute a great deal of interest for both scientists and industry. However, EPNs are restricted in their infectivity, persistence, storage, and cost of production to further broaden their application and satisfy their increasing demand. Initial EPNs improvement attempts using artificial selection and classical genetic techniques lacked both stability and effectiveness in the field, and could result in the reduction of other traits or of the overall fitness. Therefore, the EPNs genomics supported by modern genetic and molecular tools are regarded as valuable alternatives; and a continuous search for new isolates with significant behavioural and physiological characteristics can help to improve this. In South Africa (SA) although various studies have revealed an incredible richness of EPNs fauna with potential use as biocontrol agents adapted to some soil texture and environmental conditions, and underlined the value of conducting more intensive surveys in natural and different parts of the country, few studies have been done in Limpopo province. In this study, an EPN isolate, Heterorhabditis zealandica strain ETL, isolated from the northernmost region of South Africa in Bela-Bela, Limpopo province is described, and studied against late-instar of Galleria mellonella L. and Tenebrio mollitor (L.) larvae. The bacterium Photorhabdus heterorhabditis stain ETL, vectored by the EPN H. zealandica, is also described; and bacterial antimicrobial activities against human pathogenic bacteria and toxigenic fungal species studied. Additionally, the chemical characteristics of the bacterial secondary metabolites were analysed using Gas Chromatography-Mass Spectrometry. Furthermore, because the genome sequences of entomopathogenic nematode bacteria (EPNB) and their functional analyses can lead to the genetic engineering of the bacteria for use as biocontrol agents, P. heterorhabditis genome was studied to reveal information that can be useful in the design of improvement strategies for the EPNB-based pesticides. It has a genome size of 4,866,148 bp and G+C content of 42.4% similar to other Photorhabdus. It contains 4,351 protein coding genes (CDSs) of which, at least 84% are shared with the de facto type strain P. luminescens subsp. laumondii TTO1, and has 318 unknown CDSs and the genome has a higher degree of plasticity allowing it to adapt to different environmental conditions, and to be virulent against various insects...
D.Tech. (Biotechnology and Food Technology)